Stretch bending method and device, including workpiece attaching means transversely offset relative to neutral plane of workpieces



2 Sheets-Sheet l R. BENTLEY STRETCH BENDING METHOD AND DEVICE INCLUDINGWORKPIECE ATTACHING MEANS TRANSVERSELY OFFSET RELATIVE TO NEUTRAL PLANE OF WORKPIECES March 8, 1949.

Filed June 20, 1944.

INVENTOR Rowland Berkley ATTORNEY March 8, 1949. R. BENTL 2,464,169

STRETCH BENDING METHOD A DEV C INCLUDING WO IECE ATTACHING ME TRA ERSELY O E ELAT E TO NE AL PLANE OF WOR E Filed June 20, 1944 2 Sheets-Sheet 2 in 1mm uuum (ll ([4 33 S15 x A MM "-11 34H \Hll \HH lHHHH i8 12 i2 18 G5 6 INVENTOR Rowland Bentley A TTORNE Y Patented Mar. 8, 1949 UNITED STATES iih i'i'hl t'i' QFFICE PIECES Rowland Bentley, Fort Washington, Pa, assignor to The Budd Company, Philadelphia, Pa a corporation of Pennsylvania Application June 20, 1944, Serial No. 541,189

3 Claim l The invention relates to stretch bending; that-is, in curving profiles by stretching or simultaneously bending and stretching a workpiece over adie. The invention relates-also to equipment for carrying out the new process.

The outstanding object of the invention is the avoidance of over-stretching on the convex side of the curvatures which the hitherto customary procedure necessitated.

The object of the invention is achieved mainly by exerting during the forming operation a greater stretching force on the concaveiy curved-side of the'workpiece than on the convex side thereof.

The'invention and its objects and advantages will be more fully understood from the attached. drawing and the following description of an embodiment:

In the drawing,

Figure l is a diagrammatic side elevation, certain' parts in section and others broken away, or a stretch bending machine equipped for carrying out the invention;

Figure 2 is a section through the bending die and a workpiece along line 2-2 of Figure 1, but on a larger scale;

Figure 3 is a fragmentary side elevation of the workpiece diagrammatically showing the stresses applied to the workpiece by simple bending, by customary stretching and bending, and by the stretch bending according to the invention;

Figure 4 is a side elevation of one of the vises shown in Figure 1 on a larger scale, partly in section; and

5 is a fragmentary section along line 55 and on the scale of Figure 4; and

Figure 6 is a fragmentary section along line E36 of Figure 5.

The machine illustrated in Figure 1 has a base plate lil supporting a hydraulic cylinder H and integrally connected to two pairs of vertical Webs i2. A piston l3 in the cylinder H has a piston rod 14 the upper end of which carries a plate l5 adapted for the support of a forming die 16.

Between each pair of webs i2 is arranged a vise ['5 provided with laterally extending pins 18 which are rotatably supported in corresponding holes or bearings of the webs 12. The Vises H are adapted for firmly gripping the ends of a workpiece !9 by means of jaws which are not shown; the jaws and the screws or bolts 28 for tightening them may be of any appropriate construction.

While the machine is merely diagrammatically shown, because as a whole it does not constitute improvements in would a feature of the invention, it may well'be of-more elaborate construction.

The machine is used as follows:

A straight or pre-b-ent workpiece is has itsends secured in the vises i so that it extends over the with its forced upwardly so that the workpiece I9 is stretched beyond its elastic limit and retains;

after removal'frorn the machine, the exact form given to the working surface of the die. The rotatable attachment of the vises it permits the adjustment of the same in the tangentialdirection of the end portions of the die Hi, as illustrated in Figure 1.

With a customary machine, the neutral axis intersecting line at the end of the workpiece-- the plane of the axis about which the be in adjacent vise swings. Consequently, the tension exerted on the workpiece by the movement of the die is about equally distributed over the cross section of the workpiece. If this equal stretching is superimposed on the stresses indicated by the lines 23 caused by the mere bending of the workpiece, the stresses result which are diagrammatically indicated by the lines 24. So as to obtain a permanent setting by stretching, it is obviousiy necessary to stretch the workpiece to such an extent that it is stretched also on the concave side at 25 beyond the elastic limit, with the result that the stretch on the convex side at 26 is substantially greater than required for attaining a permanent setting in this region. This condition may lead to an objectionable overstressing on the convex side, over-stressing to such an extent that it impairs the strength of the workpiece.

The aforesaid shortcomings of the known procedures are overcome or alleviated by superimposing on the bending stresses a stretching force which is greater on the concave side of the workpiece than on the convex side thereof. The resultant stress diagram is indicated by the lines 2i. It will be noted that the imaginary neutral axis, intersecting line 28, is moved far inwardly in the stress diagram according to the invention, as compared with the imaginary neutral axis on line 29 of the stress diagram of the ordinary stretch bending procedure.

It will be understood that the lines 22, 28 and 29 represent the loci of the neutral axes for all points along the length of the workpiece.

The lines 23 may be called bending stress lines and the lines 24 and 2'! elongation-stress lines. Note that the angle between the neutral plane 22 and the lines 23 and 24, respectively, are about equal, whereas the angles between said plane 22 and the elongation stress lines 21 is closer to 90 than the angles between the bending stress lines 23 and said plane 22.

The desired distribution or equalization of the stresses may be obtained by arranging the swivel axis 39 for the Vises eccentrically with respect to the neutral plane 22 of the workpiece toward the concave side of the latter. The proper eccentricity has to be determined for each material, cross section and form.

The vise illustrated in the drawing has its pins l8 respectively adjustable transversely to the direction of the end of the workpiece. This ad justment is achieved by providing the pins I8 on a block 3| extending through the hollow interior 32 of the vise body and slidably guided in slots 33 communicating with said interior and the outside. The block 31 is screw threaded for receiving a threaded spindle 34 which has its ends rotatably supported respectively in plate 35 secured to one wall and in the opposite Wall of the body of the vise I1. At least one of the ends of the spindle 34 has :a square head 33 permitting the turning of the spindle so as to transversely move and adjust the block 3| together with its pins H3.

The eccentric arrangement of the axes 30 of the Vises relative to the neutral plane 22 of the workpiece obviously causes the exertion of greater stresses on that side of the plane 22 on which the axes 30 are located.

The invention is not restricted to the illustrated embodiment but many of the described features may be modified or substituted without departing from the spirit of the invention. All modifications and adaptations of the invention are intended to be covered by the claims.

Lil

What is claimed is:

1. In a method of forming a workpiece by gripping its ends and bending and stretching it over a die having a curved working surface, the feature of exerting at the ends of the workpiece a greater stretching force on the concave side than on the convex side thereof so as to equalize the resultant stretch exerted on the workpiece by the stretching proper and by the bending.

2. Vise for stretch bending'machines provided, with means for clamping it to the end of a w0rkpiece and means for attaching it to the machine freely swingable about an axis transversely ofiset relative to the neutral plane of the workpiece.

3. Vise for stretcher presses comprising a journal for securing the vise to the machine swingably about an axis extending transversely to the neutral plane of a workpiece to be secured to the vise, and means for transversely moving and adjusting the axis of the journal relative to said neutral plane. I

ROWLAND BENTLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,504,106 Dornier Aug. 5, 1924 1,761,888 Junkers June 3, 1930 1,968,010 Bailey July 31, 1934 2,269,549 Oeckl Jan. 13, 1942 2,292,731 Amiot Aug. 11, 1942 2,301,960 Lermont et a1 Nov. 17, 1942 2,326,470 Lermont Aug. 10, 1943 2,357,027 Seifried Aug. 29, 1944 FOREIGN PATENTS Number Country Date 512,266 Great Britain Aug. 31, 1939 

